Coryneform bacteria are microorganisms producing L-amino acids such as L-gtutamic acid or L-lysine in a great amount and breeding for them has been conducted with an aim of improving the productivity of L-amino acids. Various studies have been made and reported so far for breeding of amino acid-producing bacteria using gene manipulation technology (Biotechnology letters, 2 (1980) 525-530, Appln. Environ. Microbiol., 144 (1979) 181-190, Abstract of Lecture for the Meeting of the Society of Agricultural Chemistry of Japan (1981) 8). However, all of them have been directed to the improvement of the productivity of amino acid per cell by utilizing genes in amino acid biosynthetic systems as materials and enhancing them and not directed to the improvement of the productivity by analyzing the function of a cell surface structure.
By the way, when an amino acid is produced by a fermentation process, ion exchange chromatography has usually been conducted in the course of purifying a produced amino acid but, if bacterial cells remain in a fermentation medium, an ion exchange resin column is clogged when the fermentation medium is passed through the column and, accordingly, a step of removing the bacterial cells from the fermentation medium is necessary. The step is usually conducted by centrifugation, filtration or the like and it will be extremely useful industrially if such cell separating operation can be saved or simplified.
It has been known that microbial cells are precipitated in the medium due to aggregation or the like after cultivation depending on the kind of microorganisms and separation of the cells from a culture medium is extremely easy for such microorganisms. However, no Coryneform bacteria used in amino acid production, having such a property have yet been reported and a method of providing microbial cells with aggregating or precipitating property has not yet been known as well.
The published pamphlet of WO 93/03158 discloses a novel cell surface layer protein similar to a K-protein of the present invention, but this protein is clearly distinguished from the K-protein. Further, this publication discloses a protein expression-secretion system utilizing a signal peptides of the cell surface layer protein but it has not yet been known that such protein contributes to incorporation of nutrients of Coryneform bacteria and aggregating nature of bacterial cells.
Further, while Coryneform bacteria have been used industrially as L-amino acid-producing bacteria, it has been found recently that the bacteria are highly secretory and there has been an attempt of utilizing them for the production of different protein already put to practical use for Bacilli. The above-mentioned international publication WO 93/03158 also discloses a technology of such kind.
The subject to be dissolved by the present invention is to obtain a novel cell surface layer protein that contributes to the incorporation of nutrients of Coryneform bacteria and a gene thereof, and obtain a transformant obtained by amplification of the gene in the cell of Coryneform bacteria. The present invention also has a subject of using Coryneform bacteria having an activity to produce useful substances such as L-amino acids as a host for the transformant and improving the process for producing the useful substances such as L-amino acids by fermentation processes using the above-mentioned host bacteria, as well as obtaining Coryneform bacteria having a aggregating property, which is deficient in the novel cell surface layer protein, to simplify a process of amino acid production.